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The incorrect insect egg model relied too much on model organisms


Just now, we mentioned, at Nature: Researcher smashes conventional evolution doctrine about insect egg shapes. He sees that part of the problem with the old theory was the relative ease of working with model organisms:

from Placazoan Ponderings

Mikael Krauze, whose blog is Placazoan Ponderings, explains about the model organisms:

… an overreliance on them leads one to underestimate the complexity of early life forms.

Model organisms are chosen for how easy they are to handle, how fast they reproduce, and how well they manage laboratory conditions. If you need 500 mammals for an experiment, it goes without saying that using mice is much easier than using elephants.

The problem is that organisms that are fast reproducers are prone to experience streamlining selection and reductive evolution. The less stuff an organism has, the faster it can complete the development from single cell to adult.

So the organisms we have chosen to represent invertebrates, like C. elegans and D. melanogaster, are simpler than the average invertebrate. And this means that we’re likely underestimating the complexity of the last common ancestor of animals (Metazoa), as any gene found exclusively in vertebrates is thought to be a vertebrate innovation.

Attempts to correct for this bias has found that the last common Metazoan ancestor was surprisingly complex, seemingly ‘overdesigned’ for its simple morphology:

“A significant proportion of mammalian genes are not represented in the genomes of Drosophila, Caenorhabditis or Saccharomyces, and many of these are assumed to have been vertebrate innovations. To test this assumption, we conducted a preliminary EST project on the anthozoan cnidarian, Acropora millepora, a basal metazoan. More than 10% of the Acropora ESTs with strong metazoan matches to the databases had clear human homologs but were not represented in the Drosophila or Caenorhabditis genomes; this category includes a surprising diversity of transcription factors and metabolic proteins that were previously assumed to be restricted to vertebrates. Consistent with higher rates of divergence in the model invertebrates, three-way comparisons show that most Acropora ESTs match human sequences much more strongly than they do any Drosophila or Caenorhabditis sequence. Gene loss has thus been much more extensive in the model invertebrate lineages than previously assumed and, as a consequence, some genes formerly thought to be vertebrate inventions must have been present in the common metazoan ancestor. The complexity of the Acropora genome is paradoxical, given that this organism contains apparently few tissue types and the simplest extant nervous system consisting of a morphologically homogeneous nerve net.”

Kortschak R.D., et al., “EST Analysis of the Cnidarian Acropora millepora Reveals Extensive Gene Loss and Rapid Sequence Divergence in the Model Invertebrates”, Current Biology 13(24 ):2190-2195 (2003)

See also: At Nature: Researcher smashes conventional evolution doctrine about insect egg shapes The new findings almost put the egg in charge of its own shape, not what anyone expected to hear.

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